The operation of extrusion blow molding plastic products usually involves using mold tools which comprise two mold halves which are of a mutually complementary configuration and which jointly define a mold cavity. A thermoplastic extrudate, generally in the form of a tube, is placed between the opened halves of the tool. The tool closes around the preform and the preform is applied within the tool against the inside wall of the cavity formed by the tool so that the finished article is of an external configuration corresponding to the internal contour of the mold tool. Shaping of the preform within the cavity of the tool is effected either by expansion of the preform by means of gas pressure or by causing the preform to apply to the inside wall of the tool by means of reduced pressure which is produced by way of passages in the inside wall of the mold.
It is equally known for extrudates in web form or band form to be continuously extruded above the opened tool into the tool or for the extrudates to be removed from an extruder by means of a manipulator while in a still plastic condition and introduced between the opened portions of the tool.
By virtue of the shaping effect by expansion by means of an increased internal pressure or by virtue of applying the preform against the inside wall of the mold by means of vacuum, the extrusion blow molding process is basically not suitable for the production of those parts which are to involve slight wall thickness tolerances. In addition parts with severely undercut configurations are difficult to produce. Therefore in relation to many hollow bodies parts such as for example screwthreads, holding handles or the like are produced in the form of separate components and molded to the hollow body in the procedure for shaping the hollow body within the mold. Such parts are generally referred to as insert portions. It is also known for labels to be produced in the form of insert portions (in-mold labeling). For that purpose the insert portion is placed in the mold by means of a manipulator prior to the introduction of the preform.
If components are to be placed within the product as it is being produced the portion in question is also placed by means of a manipulator or holder between the opened mold halves in such a way that the generally tubular extrudate surrounds the component which is to be blow molded therearound. The mold or the tool then closes around the tube and around the component received thereby. The use of manipulators is rather troublesome in terms of their integration into the production cycle.
The object of the invention is therefore that of providing a novel process for the production of extrusion blow molded products, in which in particular the introduction of insert portions is comparatively simply integrated into the process.